Timing device



Sept. 1941-Y K. V. KEELEY 2,256,117

TIMING DEVICE Filed Feb. 12, 1958 switch independent of the period the'switch.

scribed.

Patented Sept. 16, 1941 UNITED STATES PATENT OFFICE Kedric V. Keeley, Angeles, Calif.

Application February 1S er1l;elNo. 190,304

Claims.

This invention relates broadly to timing devices, and particularly to non-mechanical timing devices distinct from clock movements, and the like. More specifically, the invention relates to a-timing device which depends upon the thermal inertia of a. vacuum tube element.

An object of the invention is to provide a tim-- ing. device capable of controlling an electric circult for a predetermined relatively shortperiod with fair accuracy and without the use of'mechanical moving mechanisms, such as clock works.

Another obiectis to provide a timing device which may be employed in connection with any closure switch in an electrical circuit for closing or opening asecond circuit for a fixed period of time following actuation of the first mentioned of closure of Another object is to provide a timing switch a. vacuum tube 6.. The-circuit between the power line 2 and the primary winding 2 of the transformer is normally interrupted by switch conadapted .to close or open a work circuit for short fixed intervals at predetermined different hours of the day with a relatively simple and inexpensive equipment. I

The invention will be explained by describing in detail a system and apparatus incorporating the invention, specifically adapted for ringing bells in schools, and the like, at the periods of commencement of diiierent classes. It will be understood, however, that the invention is adaptable to other specific systems and is not to be limited to the specific system shown and de- Inthe drawing:

Fig. 1 is an elevation view of a clock switch incorporating my invention, adapted to recurrently close a bell circuit, or the like, for short intervals of time; I Fig. 2 is a sectional view, taken in the plane II-II of Fig. 1

3 is a greatly enlarged detail view of the contact mechanism of the clock shown in Fig. 1;

Fig. 4 is a schematic diagram showing the electrical circuit employed: and

.5 isan enlarged detail view of the switch mechanism, the view being taken at right angles to the view of Fig. 3.

Referring first to Fig. 4, there is shown a stepdown transformer I having a primary winding 2 adapted to be energized from a suitable source of alternating current, such as a commercial power line 2, and having a secondary winding 4 of a suitable number of turns in proportion to the number of turns in winding 2 to supply a proper voltage for energizing the cathode I of tacts I so that the cathode 5' of the vacuum tube is normally de-energized and cold. The vacuum tube 6 also has an anode 8 which is connected through the winding 9 of a relay ill to the power 4 side of the switch I.

As shown in Fig. 4, the relay I0 is provided with contacts II which are normally open when the relay I0 is not energized, but closed'in response to energization of the relay. Thus the contacts Ii are shown connected in series with a battery I2 and an electric bell I3; Obviously, any other source of electric power may be employed instead of the battery I2.

Under normal conditions of operation, when the switch 1 is open, the relay in is tie-energized because it can receive current only through the vacuum tube 6 and when the cathode 5 of the tube iscold no current can flow through the tube. As previously indicated, the cathode 5 is cold when the switch 1 is open because no current is flowing in the primary winding 2 of the I transformer.

Now assume that the switch I is closed, thereby completing a circuit from the power line 3 to the primary winding 2 of the transformer.

This causes current to flow in the primary windlog 2, inducing current in the seconda y W nding 4, which heats the cathode i of the vacuumtube 6, thereby rendering the tube conductive. However, no current flows from the cathode to the anode of' the tube I at this. time the winding 9 is connected directly inseries between the anode 8 and the cathode I through the contacts of the switch I, a conductor i4 interconnecting the switch end of the primary winding 2 to the cathode 5'. Therefore the relay ill remains de-energized following the closure. of

switch contacts 1, although the cathode I of the tube [remains heated. However, when the switch contacts 1 are opened, a circuit from the powerline 2 to the winding 8 of relay ll is'completed and maintained for a brief period of time, due to the thermal inertia of the. cathode 5. Thus a circuit path can be traced from the upper side of power line 2'through the primary winding 2 of the transformer I through conductor I4, the cathode 5 and anode l of tube 6 and winding 9 back to the lower side of the power line 2. Of course the primary winding 2 of transformer I offers some impedance to the flow of current through this circuit, but the impedance of winding 2 can readily be made low enough. as

compared to the impedance offered by the tube 6 and the relay winding 9 so that sufficient current will flow while the cathode is heated to energize relay Ill. Energization of relay III, of course, closes contact and rings the bell I3, the latter: continuing to ring until the relaylll is again de-energized. Relay ID will be de-energized as soon as the cathode 5 cools off to a point where its electron emission is insufilcient to supand an anode. It is possible, however, that for specific applications it may be desirable to employ a tube having other electrodes in addition to the cathode and anode;

The circuit described with reference to Fig. 4

lends itself admirably to use in. a bell-ringing system for schools, factories, and the like, in

which the switch contacts 1 are closed and opened" at predetermined hours of the day by a clock mechanism. The system is particularly adapted for such use because the time of closure of the bell circuit is quite independent of the period of closure of the contacts 1, and it is quite easy to construct a'clock switch that will open a pair of contacts at fairly accurate time intervals whereas it is more difiicult and expensive to construct clock-actuated switches which not only close at predetermined hours of the day, but also remain closed for an accurately measured short interval of time.

Referring now to Fig. 1, there is depicted a complete apparatus for closing a circuit, such as a bell circuit, for fixed intervals of time at predetermined hours of the day. As shown in Fig. 1, the apparatus comprises a cabinet 2|) in which are mounted the transformer the vacuum tube 6, the relay l0 and a clock mechanism 2| incorpbrating the switch contacts 1.

The clock mechanism proper may be of any well-known type, and neednot be described in detail. As shown to best advantage in Fig. 2, the particular mechanism shown is of the electrical type employing a motor 22 actuating a train of gears which rotate the hands 23. The shaft 24 of one of the gears is extended rearwardly and mounts a pair of sprockets 25 and 26 which support and drive an endless chain 21. Thus the chain, after passing over the sprocket 26, passes down under an'idler sprocket 28, thence up over the sprocket 25, thence down under a second idler sprocket 23 and then'back over sprocket 26 again. By employingthe two sprockets 25 and 26 and the idler sprockets 28 and 29 spaced a substantial distance therefrom, a relatively long chain may be employed, which requires a correspondingly long time to pass through a complete cycle, although its linear speed may be relatively great. It is desirable to have a high linear speed onthe chain because it carries elements for actuating the switch .mechanism and if the chain moves rapidly, it is possible -to obtain greater accuracy in the timing of the contact closure. 0bviously, if necessary or desirable, a' larger number'of sprockets may be employed. Thus three and 5, .a pairof resilient strip members 36 and drive sprockets and three idler sprockets, or four drive sprockets and four idler sprockets might be employed.

The switch contacts 1 are positioned above the sprockets 25 and comprise, as shown in Figs. 3

3|, respectively, supported at one end between insulating blocks 32 and carrying juxtaposed contacting points 33 and 34. Each of the strips also has insulatingly attached thereto a cam follower. Thus the upper strip 30 has a follower 35 insulatingly secured thereto and the contact strip 3| has a follower 36 secured thereto. .These followers 36 terminate at their lower ends in transverse surfaces positioned closely adjacent to each other immediately above the path of the chain 21 on the sprocket 25. The'sprocket 25 is provided at spaced intervals therealong with outwardly projecting rearwardly extending cam wires 31, these cams being so spaced along the chain as to contact the cam followers 35 and 36 at predetermined desired intervals. As shown, the cams 31 are so spaced as to pass under the cam followers at each hour at definite intervals, such as 5 or 10 minutes, after the hour.

As each of the cams 31 passes under the cam followers 35 and,36 it first lifts both cam followers by substantially equal amounts to carry the contact strips 30 and 3| both upwardly while maintaining. them in spaced apart relation. However, a the cam 31 continues its motion it releases the cam follower 35 a. few seconds before it releases the cam follower 36, thereby permitting the contact strip 30 to drop while the contact strip 3| is still held in uppermost positionfliausing closure of the contact points 33 and 34. As the chain continues its motion, the cam 31 passes away from the cam follower 36, permitting it to release and again open the contact points 33 and 34.,

With the-chain mechanism of the type described, it is easy to close the contacts 1 at desired periods during the day and maintain them closed for an appreciable interval of time sufficient to heat the cathode 5 of the tube 6 and thereby energize the relay H) for an accurately measured period of time, as previously described having a thermionic cathode and an anode, the

cathode being adapted to be electrically heated, a current source, a device adapted to beenergized from said source, an energizing circuit for said cathode to heat the same, and means for substantially simultaneously interrupting flow of heating current to said cathode and completing an electrical circuit including said source, said tube and said device in series, whereby current flows in said series circuit to energize said device only while said'cathode remains heated'following interruption of heating current thereto.

,2. In combination, a vacuum tube having a thermionic cathode and an anode, the cathode being adapted to be electrically heated, a current source, a deviceadapted to be energized from said source, and means for successively applying current from said source to said cathode to heat it above an electron-emitting temperature and then through said tube to said device whereby current flows in said device to energize it only while said cathode remains. heated following interruption of heating current thereto.

3. In combination, avacuum tube having a while said cathode remains heated to owing 20 completion oi said series circuit.

4. An electrical system comprising a switch, a current source, a current-actuated device and means responsive to closing and opening of said switch for supplying current from said source to said device for a fixed length of time only immediately following the opening of said switch, said fixed length 01! time being determined by said means and being substantially independent of the electrical characteristics of said device.

5. A system comprising a switch and means for periodically recurrently closing it for a period of time and then opening it for a period or time exceeding a predetermined minimum, a current source, a current-actuated device, and means responsive to said closing and said open ing of said switch for supplying current from said source to said device following said opening 'of said switch, for a predetermined time less than said predetermined minimum.

KEDRIC V. KEEILEY. 

